This invention is generally in the field of combustion apparatus for burning fuels, and particularly combustion systems for creating steam and/or electric energy, and more particularly to combustions systems using waste products as a fuel source and waste disposal means.
Production of Electrical Power and Pollution
Electricity has conventionally been produced at power plants by electrical generators driven by gas turbines, steam turbines, hydroelectric dams, and large diesel engines. The steam use in these plants conventionally has been created by burning coal, oil or natural gas, or by nuclear reactors.
The world is currently facing a persistent and complex energy and electrical power crisis. Over the past 10 years, electrical power demand has increased by about 30%, while transmission capacity has increased only half that much. The demand for electricity and for the fuel used to produce electricity is projected to increase. With the worldwide growth of energy demand, sensible energy policy requires the careful balancing of three objectives: (a) low cost; (b) minimal environmental impact; and (c) security of supply. Energy security depends upon an ability to properly manage the economics, supply and environmental consequences of the energy sources used to produce electricity.
The United States currently produces electricity using several different fuels, including coal, which represents about 57% of the electrical supply, and nuclear energy, which represents about 20% of the electrical supply. The remainder is provided by natural gas-fired power plants, hydroelectric dams, and small amounts of renewable energy. Solar and fuel cell technologies are currently underdeveloped, and are expensive. Hydroelectric and wind powers are disadvantageously limited in use by geographic location. The energy industry has long been seeking more environmentally friendly, efficient, safe and cost effective alternatives to coal, natural gas and nuclear energy.
Coal-Burning Power Plants
Coal is a nonrenewable resource, and only approximately 200 years of mineable coal is left. The burning of coal is generally only about 20% efficient (only about 20% of the BTUs per pound in the coal are actually used to convert water into steam). Currently, some 40 million tons of coal are used annually for power generation.
Coal-burning power plants release millions of tons of toxic emissions into the atmosphere each year. The United States Public Interest Research Group recently reported that power plant air pollution is increasing, with a significant amount of the increase coming from coal-burning plants. While coal is relatively inexpensive to burn, it is one of the most impure fuels. Burned coal produces millions of pounds of “coal ash” and “fly ash,” solid combustion waste materials that contain highly poisonous and/or radioactive chemicals, such as arsenic, uranium, mercury, lead and thorium. (The ash content ranges from about 5% to 15% of coal burned.)
Other environmental pollutants produced by conventional combustion-based power generation plants include sulfur dioxide (SO2); other oxides of sulfur, such as SO, SO2 and/or SO3, collectively known as SOx; nitrogen dioxide (NO2), the major component in smog; nitric oxide (NO); other oxides of nitrogen, such as NO, N2O and/or NO2, collectively known as NOx; carbon monoxide (CO); carbon dioxide (CO2); methane (CH4); hydrochloric acid (HCl); dioxin; volatile organic compounds (VOCs), which cause smog and are harmful to plants and animals; various metals, such as zinc, thallium, cadmium, nickel and chromium; radioactive materials other than the isotopes uranium and thorium, such as radium, radon, polonium, bismuth and lead; other carcinogenic and/or mutagenic substances; and particulate matter, which is a criteria air pollutant.
Conventional coal-burning plants use air as the source of oxygen for combustion. However, air contains 76.9% by weight nitrogen (N2) and 23.1% by weight oxygen (O2), as well as some argon and CO2. These non-oxygen components make air a non-ideal source for oxygen, as they can contribute to environmental pollutants, such as NOx, SOx, and CO.
Current U.S. regulatory requirements prescribe the amounts of atmospheric emissions that are permitted in particular locations by given power-generating plants. Allowable emission threshold levels are continually being decreased, which is placing increasing pressure on power-generating plants to reduce emissions.
Natural Gas Power Plants
Compared to coal and nuclear power plants, conventional natural gas-fueled power plants can be built at a relatively low cost. However, disadvantageously, these plants are extremely sensitive to increases in the price of fuel, which frequently occur as a result of problems with supply. Further, the burning of natural gas by conventional methods is generally only about 30% efficient (only about 30% of the energy value of the natural gas is actually used to convert water into steam). Moreover, high levels of the criteria air pollutant NOx are often emitted into the atmosphere from conventional natural gas-fueled power plants.
Inefficiency of Conventional Power Generation
The conventional generation of electrical power and heat separately (as opposed to cogeneration, trigeneration, and the like) is generally inherently inefficient, only converting about one third of a fuel's potential energy into usable energy. For example, traditional coal, oil or natural gas fired thermal generating stations generally do not convert more than about one third of the fuel's initial energy into useful electricity; the remainder is discarded as waste heat. There is a present need for safe, rapid, inexpensive, efficient and environmentally clean methods and apparatus for producing electrical power, and for producing steam and combustion gas exhaust products that can be used in the production of electrical power.
Disposal of Waste and Hazardous Materials
There is continuously an abundant supply of hydrocarbon waste materials on the earth. Every year, nearly 1600 pounds of trash are discarded per person, about 80% of which is placed into landfills. The landfill decomposition rates for many of these hydrocarbon materials are tens to hundreds of years. Scrap tires, plastic waste and textile and carpet waste are three types of hydrocarbon waste materials often placed into landfills.
Approximately 270 million tires (3.4 million tons) are discarded as scrap tires each year in the United States, with roughly 800 million tires waiting to be placed into landfills. Many states have banned the placement of whole tires and/or partial scrap tires in landfills. In order to avoid disposal fees or the effort required to legally dispose of scrap tires, many scrap tires are illegally dumped. These illegally dumped tires pose health and environmental problems, are unsightly, and create fire hazards. Adequate methods for properly disposing of scrap tires do not currently exist.
Approximately 75 billion pounds of plastic are produced each year in the United States. Examples of these plastics include polyethylene containers and products. The majority of plastic ends up in landfills, where decomposition takes many years. It would be desirable to provide better means of disposing of waste plastic.
The amount of carpet entering the waste stream is steadily increasing. About 96% of this waste is disposed in land fills. According to U.S. Environmental Protection Agency (EPA), approximately 14 billion pounds of textile and carpet waste is landfilled each year in the United States. Carpet takes over 50 years to begin to decompose, landfill space is diminishing, and many landfills no longer accept carpet. It would be desirable to provide better means of disposing of waste carpet.
There is currently a need for methods and apparatus to eliminate scrap tires and plastic, carpet textile and other hydrocarbon waste materials in a safe, rapid, inexpensive, efficient and environmentally clean manner.
There also is an increasing need to dispose of hazardous materials in a safe, effective, efficient, and cost effective manner. Examples of hazardous materials include infectious medical wastes; biological and chemical weapons, such as anthrax, nerve agents, and rockets or containment devices therefor; and hazardous air pollutants. The proper disposal of such materials is expensive and generally present a serious risk to the health of humans and other animals. Existing means for safely disposing of hazardous materials are undesirable. In many cases, this has entailed the dumping of the hazardous materials into deep landfill zones or encasing it in protective containers and then burying these containers in landfills or at sea. Other hazardous materials are disposed of by burning at trash dumps or commercial furnaces. However, depending upon the burning parameters, such destruction frequently is time-consuming, incomplete, and produces dangerous levels of noxious environmental pollutants. There exists a need for safe, rapid, inexpensive and efficient methods and apparatuses for the complete destruction of hazardous materials (rendering them non-hazardous) without producing unacceptable levels of environmental pollutants.